gerrit's blog

Yesterday I finished the mechanical construction of my RepRap Mendel 3D printer. This had been quite some work.  I had to drill pretty much every hole of my rapid-prototyped parts due to the moderate print quality of my Repstrap. But in the end the machine looks really nice, I think. All the thick sheets are made of acrylic instead of wood.

For the electronics part I decided to build the Pololu stepper driver board (which can be found in the reprap subversion repository) as a replacement for the standard gen 3 RepRap/Makerbot electronics. This option is much cheaper and much easier to build at home because of the fact that the pcbs have only one layer. I have tried to etch the pcbs for the gen 3 electronics at home as well but had to realize in the process that creating vias (connections from one layer to another) manually is really a pain. Furthermore I made a Sanguino-like microcontroller board for controlling everything. Getting my micocontroller board to work with the RepRap firmware and the stepper board required some hacking. It would probably have been easier to just use a Arduino Mega which seems to be the common choice in combination with Pololu stepper drivers.. Oh and I rerouted the optoendstop pcb to fit on one layer which was really straightforward.

In order to get the Mendel running and printing there is still some work to do, fine tuning of the belts etc and I am missing a stepper motor but I won't be home the next three weeks, so this will have to wait.

I have successfully repaired the plastic extruder of my repstrap 3d printer. I had to buy a cheap drill press in order to process the raw ptfe and the brass barrel. It seems to be really hard to drill straight though the brass barrel without a drill press (or maybe my drill wasn't good...).

This time I wanted to make sure that the brass barrel couldn't slip out of the thermal barrier again, so I secured the brass barrel in place with a nut and a square piece of ptfe, which is attached to the wood frame with two screws.

As you can see on the picture below I printed a complete set of parts for Wade's extruder (www.thingiverse.com/thing:1794). 

The print quality is still not perfect but I think it is usable and sufficient for printing the RepRap Mendel parts. I started printing Mendel parts already. The only problem remaining is warping, I don't think I can avoid this without a heated printing bed. But it is not that bad yet, so I hope to get along without a heated bed untill I have a working Mendel.

3d printer in action from Gerrit Wyen on Vimeo.

I have a hard time with my plastic extruder. Building it was mostly straightforward but reliably using it is not.

The extruder nozzle, the brass barrel and the PTFE heat barrier, which are the main components of a plastic extruder, did I buy from the MakerBot webshop (took a few weeks to arrive, the German custom is really slow in handling packages...).

As one can see on the picture I built a simple wood construction to hold those parts, drilled some holes for the plastic filament and added a stepper motor plus a ball bearing for being able to guide the filament to the extruder nozzle.

At the beginning the extruder worked more or less flawlessly, but then the nozzle clogged up and the motor stalled.( The PLA plastic tends to do that from time to time as I read. )
I had to learn the hard way that employing manual force to push the filament through the extruder is NOT a good idea.. I pushed the brass barrel out of the ptfe barrier (PTFE expands when it is heated up) and ruined the threads inside of it.
As a quick fix I added a nut to the brass barrel and glued it onto the PTFE with JB Weld.

But after really little use the adhesive joint broke apart.

Here are two pictures of my print results so far. I tried to print a Shot Glass that I got from Thingiverse.

The bad quality of the prints was mostly the result of software issues (irregular movement of the extruder stepper and a bad ration to the feed rate, loss of the serial connection etc).
I think I fixed most of those problems but can't really verify it till the extruder is working again.

Today I ordered some raw PTFE that will hopefully arrive soon. Once I get it I might be able to fix the extruder and get back printing again.

I didn't build the plastic extruder yet but everything else of my Tommelise is working already. The stepper motors are now powered by three TMC-222-SI driver chips which communicate over TWI/I2C with my ATMega 164p microcontroller. Using I2C driver chips, instead of the ones that I found in the old printers that I dissembled, saved me a lot of cabling plus they support microstepping.

For testing purpose I attached a milling machine as a tool head:

As an easy shape to start with I chose to mill a star.
For doing that, I first drew a star in gimp, reduced the color palette to black/white and saved it as a png image.

After that I wrote a small python script that looks for black pixels in the image and sends the microcontroller the command to mill a hole at the corresponding location.

It turned out quite well:

Of course it would have been nicer to create a real tool path instead of milling dots into the workpiece. But I will concentrate on building the plastic extruder now.

Yesterday my preordered nokia n900 finally arrived. It will replace my 3 years old samsung cellphone and my n800 internet tablet. From now on I only have to carry around one device in my pocket, which is a big advantage.
Furthermore the n900 contains a decent camera which will allow me to document the progress of my 3d printer again (the camera in my old cellphone died a few weeks ago).